In order to reduce riders' injuries in the event of a motor vehicle collision, two major safety devices have been introduced: the safety belt, and the air bag.
The safety belt prevents riders from being thrown towards the windscreen in the event of collision. This device has proven effective at low urban vehicle speeds. However, when vehicle speed increases towards the interurban speeds, the safety belt itself becomes a source of injuries. Due to the substantial inertia forces exerted on a rider's body, the abdomen and chest can be crushed by the relatively stiff belt, which prevents any relief from high decelerations exerted on the rider's body by energy absorbent displacements.
The introduction of the air bag, as a supplement to the safety belt, was intended to soften the blow from the rider-safety belt operation. Unfortunately, the short time response of the safety belt, due to its relatively high stiffness, versus the deployment time of the air bag (depending, mainly, on gas pressure generated by a pyrotechnic tablet), called for highly accelerating the air bag, to catch up with the safety belt time response, in order to ensure the simultaneous operation of both. Therefore, an extremely high air bag velocity of 320 km/h is needed for the air bag and safety belt to operate simultaneously.
The worrisome number of injuries, caused by air bags fired towards rider's chests and head, revealed the air bag as a new source of a potential hazard. Although the air bag may be considered as a contribution to the total safety of vehicle riders, some inevitable new perceptions of the whole chair, safety belt, and air bag systems must be worked out to overcome the problems which remain unsolved.
A number of solutions to the problem of deceleration forces acting on a rider during a collision have been proposed in the patent literature. For example, there is shown in U.S. Pat. No. 5,244,252 to Serber a seat assembly for a vehicle which includes a seat, a seat back, and mounting means mounting the seat for movement in fore and aft directions in the vehicle along an upwardly concave arcuate path. This seat assembly is designed to prevent "submarining", wherein the body slides away from the seat, out from under the seatbelt. The arcuate path has a radius of curvature which is sufficiently large to timely move in front of and to contain the person's buttocks so as to reduce deceleration and maintain frictional contact of the person's buttocks with the seat. The seat belt is coupled to the chassis adjacent the seat back, and the seat is not coupled to the seat back, so the effect is to fold the person's body at the waist.
There is shown in WO94/22692 to Muller, a process for reducing the forces acting on a passenger belted into a seat in a vehicle when the vehicle collides with an obstacle. The approach to an obstacle is detected and evaluated by proximity detectors acting as sensors and, when a collision is recognized as inevitable, the seat is accelerated against the collision direction, stopped at the end of its travel and, once the collision has occurred, the seat is moved in the collision direction and stopped at the end of its travel. Preferably, an airbag system is actuated at the same time as the movement of the seat, possibly by the proximity detection system.
This proposal suffers from several disadvantages. First, any proximity detector system is subject to failure or accidental actuation. If the sensor indicates there will be a collision, and there is no collision, the driver or passenger finds himself moving back within the vehicle, which can disrupt his concentration and provide difficulties returning the seat to its former position. Second, if there is not precise time correlation between the movement of the seat and the occurrence of the collision, the seat can be moving backwards at the time of impact. In this case, the forces acting on the person will be much greater than those caused by the impact alone, increasing the likelihood of injury. Third, when a driven sees he is about to crash, he will generally apply the brakes, causing his body to move forward. If he does so while the seat is moving away from the brake pedal, it can prevent effective braking of the vehicle, and also increase deceleration forces acting on his body. In addition, a linear spring is provided to absorb the energy in the piston at stop the seat at the end of its travel. However, due to bottoming, the seat will stop with a bump, in both directions.
There is shown, in Japanese laid-open publication 9-226495 (Mitsubishi), a passenger protection system for a vehicle including a seat movement unit to retreat a seat to a predetermined position on receipt of an air bag start signal. Simultaneously, a seat belt expansion unit expands a chest guard and an abdomen guard on the seat belt, which is attached to the vehicle chassis. In this system, the airbag is inflated upon impact above a threshold, at which time the vehicle seat moves away from the airbag. In this system, like that described above, the movement of the vehicle seat away from the airbag at the time of collision, increases, rather than decreases, the deceleration forces acting on the body.
A similar problem arises in the event of a rear end collision, especially which the vehicle is hit when stationary. In this case, the force of the collision causes the vehicle to accelerate in a forward direction, while the body of a rider moves backwards until it hits the back of the car seat. Due to the acceleration forces acting on the body, and the fact that the head support is generally not located in the ideal position to support the rider's head, a rider in this situation often suffers from whiplash.
Accordingly, there is a long felt need for a motor vehicle safety system which incorporates the operation of air bag and safety belt in such a way to provide maximum protection with minimum injuries from the safety devices themselves. In addition, it would be very desirable to have such a safety system which also provides protection in the event of a rear end collision.